This invention relates to new leuco compounds and the intense yellow dyes obtained therefrom by oxidation. Providing improved new dyes, particularly a new primary (yellow, red and blue) color, is continually an important objective of industrial research. Moreover, the properties required are frequently complicated by the utility envisaged. A particularly challenging task is presented by the demanding set of properties required for colors and color formers to be used in photoimaging systems.
Accordingly, it is an objective of the present invention to provide new compounds which are capable of forming intense yellow images upon oxidation. A further objective is to provide the above compounds which are particularly useful in photosensitive systems. Another objective is to attain superior neutral (gray-to-black) shades, by combining the above novel leuco with selected leuco triarylmethanes which can be oxidized to purple dyes, particularly for use in photoimaging systems.
The invention comprises compounds of the formula: ##STR5## wherein m = 0 or 1; Ar is an arylene or lower alkyl substituted arylene radical;
R.sub.1 and R.sub.2, which may be the same or different, are lower alkyl or hydroxyalkyl groups, or ##STR6## R.sub.3 is H, lower alkyl, benzyl, R.sub.4, or ##STR7## R.sub.5 is H, a C.sub.3 -C.sub.6 alkyl group, an aryl group, ##STR8## wherein n = 2-6; and R.sub.6 is a lower alkyl group or an aryl group.
Compounds of the formula, wherein m = 1, represent essentially colorless leuco dyes; they may be oxidized to their corresponding yellow dye forms, which are represented by the formula, wherein m = 0. The leuco dyes of formula 1 may be used in photosensitive image forming compositions containing a photooxidant capable of oxidizing the leuco dye, such as hexaarylbiimidazoles and N-halolophines. These leuco dyes may also be used in combination with other leucos, such as the preferred leuco triarylmethane of the following general formula: ##STR9## wherein R.sub.7, R.sub.8, R.sub.9, and R.sub.10, which may be the same or different, are lower alkyl groups. A mixture of leuco dyes of formulas 1 and 2 yields an intense black color on oxidation. Such image-forming compositions may be used to coat paper or film, as hereinafter exemplified, and may contain other ingredients appropriate for such utility, for example, solvents, plasticizers, and binders.
The leuco dyes of formula 1 and their corresponding oxidized dye forms, mixtures thereof with other leuco dyes and their corresponding oxidized dye forms, compositions containing said leuco dyes, oxidized dyes and mixtures thereof, and substrates coated with said compositions, are within the scope of this invention.